<template>
    <ul class="list">
        <li class="item"
            v-for="item of letters"
            :key="item"
            :ref="item"
            @click="handleLetterClick"
            @touchstart = "handleTouchStart"
            @touchmove = "handleTouchMove"
            @touchend = "handleTouchEnd"
            >{{item}}
        </li>
    </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },

  computed: {
    letters () {
        let letters = []
        for(let i in this.cities) {
          letters.push(i)
        }
        return letters
    }
  },

  data () {
    return {
      touchstatus: false,
      startY: 0,
      timer: null
    }
  },

  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },

  methods: {
    handleLetterClick(e){
      this.$emit('change',e.target.innerText) 
    },
    handleTouchStart(){
      this.touchstatus = true
    },
    handleTouchMove(e){
      if(this.touchstatus) {
        if(this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          let startY = this.$refs['A'][0].offsetTop
          let touchY = e.touches[0].clientY - 79
          let index = Math.floor((touchY - startY)/23)
          if(index >=0 && index < this.letters.length){
            this.$emit('change',this.letters[index])
          }
        },16)

   
      }
    },
    
    handleTouchEnd(){
      this.touchstatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    position: absolute
    right: 0
    top: 2.54rem
    bottom: 0
    width: .4rem
    display: flex
    justify-content: center
    flex-direction: column
    color: $bgcolor
    .item
      line-height: .46rem
      text-align: center
</style>